KVM: x86: virtualize cpuid faulting

Hardware support for faulting on the cpuid instruction is not required to
emulate it, because cpuid triggers a VM exit anyways. KVM handles the relevant
MSRs (MSR_PLATFORM_INFO and MSR_MISC_FEATURES_ENABLE) and upon a
cpuid-induced VM exit checks the cpuid faulting state and the CPL.
kvm_require_cpl is even kind enough to inject the GP fault for us.

Signed-off-by: Kyle Huey <khuey@kylehuey.com>
Reviewed-by: David Matlack <dmatlack@google.com>
[Return "1" from kvm_emulate_cpuid, it's not void. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

5 files changed, 49 insertions, 0 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 2cc5ec7cc6f5..f5c942edbc86 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -611,6 +611,8 @@ struct kvm_vcpu_arch {
         unsigned long dr7;
         unsigned long eff_db[KVM_NR_DB_REGS];
         unsigned long guest_debug_dr7;
+        u64 msr_platform_info;
+        u64 msr_misc_features_enables;
 
         u64 mcg_cap;
         u64 mcg_status;
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index efde6cc50875..a181ae76c71c 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -876,6 +876,9 @@ int kvm_emulate_cpuid(struct kvm_vcpu *vcpu)
 {
         u32 eax, ebx, ecx, edx;
 
+        if (cpuid_fault_enabled(vcpu) && !kvm_require_cpl(vcpu, 0))
+                return 1;
+
         eax = kvm_register_read(vcpu, VCPU_REGS_RAX);
         ecx = kvm_register_read(vcpu, VCPU_REGS_RCX);
         kvm_cpuid(vcpu, &eax, &ebx, &ecx, &edx);
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index 35058c2c0eea..a6fd40aade7c 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -205,4 +205,15 @@ static inline int guest_cpuid_stepping(struct kvm_vcpu *vcpu)
         return x86_stepping(best->eax);
 }
 
+static inline bool supports_cpuid_fault(struct kvm_vcpu *vcpu)
+{
+        return vcpu->arch.msr_platform_info & MSR_PLATFORM_INFO_CPUID_FAULT;
+}
+
+static inline bool cpuid_fault_enabled(struct kvm_vcpu *vcpu)
+{
+        return vcpu->arch.msr_misc_features_enables &
+                  MSR_MISC_FEATURES_ENABLES_CPUID_FAULT;
+}
+
 #endif
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 45c7306c8780..6a2ea945d01f 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3854,6 +3854,13 @@ static int em_sti(struct x86_emulate_ctxt *ctxt)
 static int em_cpuid(struct x86_emulate_ctxt *ctxt)
 {
         u32 eax, ebx, ecx, edx;
+        u64 msr = 0;
+
+        ctxt->ops->get_msr(ctxt, MSR_MISC_FEATURES_ENABLES, &msr);
+        if (msr & MSR_MISC_FEATURES_ENABLES_CPUID_FAULT &&
+            ctxt->ops->cpl(ctxt)) {
+                return emulate_gp(ctxt, 0);
+        }
 
         eax = reg_read(ctxt, VCPU_REGS_RAX);
         ecx = reg_read(ctxt, VCPU_REGS_RCX);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 34bf64fb4dea..49a69c0a0d50 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1007,6 +1007,8 @@ static u32 emulated_msrs[] = {
         MSR_IA32_MCG_CTL,
         MSR_IA32_MCG_EXT_CTL,
         MSR_IA32_SMBASE,
+        MSR_PLATFORM_INFO,
+        MSR_MISC_FEATURES_ENABLES,
 };
 
 static unsigned num_emulated_msrs;
@@ -2314,6 +2316,21 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
                         return 1;
                 vcpu->arch.osvw.status = data;
                 break;
+        case MSR_PLATFORM_INFO:
+                if (!msr_info->host_initiated ||
+                    data & ~MSR_PLATFORM_INFO_CPUID_FAULT ||
+                    (!(data & MSR_PLATFORM_INFO_CPUID_FAULT) &&
+                     cpuid_fault_enabled(vcpu)))
+                        return 1;
+                vcpu->arch.msr_platform_info = data;
+                break;
+        case MSR_MISC_FEATURES_ENABLES:
+                if (data & ~MSR_MISC_FEATURES_ENABLES_CPUID_FAULT ||
+                    (data & MSR_MISC_FEATURES_ENABLES_CPUID_FAULT &&
+                     !supports_cpuid_fault(vcpu)))
+                        return 1;
+                vcpu->arch.msr_misc_features_enables = data;
+                break;
         default:
                 if (msr && (msr == vcpu->kvm->arch.xen_hvm_config.msr))
                         return xen_hvm_config(vcpu, data);
@@ -2529,6 +2546,12 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
                         return 1;
                 msr_info->data = vcpu->arch.osvw.status;
                 break;
+        case MSR_PLATFORM_INFO:
+                msr_info->data = vcpu->arch.msr_platform_info;
+                break;
+        case MSR_MISC_FEATURES_ENABLES:
+                msr_info->data = vcpu->arch.msr_misc_features_enables;
+                break;
         default:
                 if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
                         return kvm_pmu_get_msr(vcpu, msr_info->index, &msr_info->data);
@@ -7710,6 +7733,9 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
         if (!init_event) {
                 kvm_pmu_reset(vcpu);
                 vcpu->arch.smbase = 0x30000;
+
+                vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT;
+                vcpu->arch.msr_misc_features_enables = 0;
         }
 
         memset(vcpu->arch.regs, 0, sizeof(vcpu->arch.regs));